DESCRIPTION: While the assembly of proteins that replicate DNA has been investigated in detail, relatively little is known about the way in which the strands of DNA are looped at the fork. Over 15 years ago, a model was proposed in which the lagging strand loops back at the fork and engages a second molecule of DNA polymerase This dimeric polymerase assembly and DNA loop was envisioned to couple leading and lagging strand replication with the proteins involved in lagging strand synthesis being recycled from the end of a completed Okazaki fragment to the next primer. Unfortunately, little direct evidence for looping exists. In the ongoing work of this laboratory, electron microscopy(EM) has been used to examine products of in vitro replication reactions. Loops of DNA at the replication fork were visualized. Understanding looping and how loops grow and reform with Okazaki fragment synthesis is the goal of this project.